: Instead of using thick solid sections, use ribs to provide structural stiffness. To avoid sink marks on the opposite surface, rib thickness should generally be of the nominal wall thickness. 2. The Feed and Ejection Systems
The mold design process typically involves the following steps:
The story: a mold maker built a beautiful tool for a clear acrylic lens. He used a tiny, pinpoint gate for aesthetic reasons. But acrylic is shear-sensitive. The plastic screamed through the tiny gate at 400 m/s, got friction-hot, and burned into brown streaks. The lens looked like a fly had died inside.
The solution was a “fan gate”—wide and thin—spreading the flow like a delta. The pressure dropped, the flow slowed, and the lens came out crystal clear.
: This is the most critical rule. Aim for consistent walls between 1–4 mm. Non-uniform walls lead to "sink marks" (surface depressions) and "warpage" because thick sections cool slower than thin ones. Draft Angles
Aris closed the notebook. He looked at his clip, then at his CAD model. He added four 0.02mm vents at the last point of fill. He adjusted the wall thickness to be uniform 2.5mm, not 2-to-5. He set the draft angle. He changed the gate to a three-pin submarine gate to balance the flow.
: Instead of using thick solid sections, use ribs to provide structural stiffness. To avoid sink marks on the opposite surface, rib thickness should generally be of the nominal wall thickness. 2. The Feed and Ejection Systems
The mold design process typically involves the following steps:
The story: a mold maker built a beautiful tool for a clear acrylic lens. He used a tiny, pinpoint gate for aesthetic reasons. But acrylic is shear-sensitive. The plastic screamed through the tiny gate at 400 m/s, got friction-hot, and burned into brown streaks. The lens looked like a fly had died inside.
The solution was a “fan gate”—wide and thin—spreading the flow like a delta. The pressure dropped, the flow slowed, and the lens came out crystal clear.
: This is the most critical rule. Aim for consistent walls between 1–4 mm. Non-uniform walls lead to "sink marks" (surface depressions) and "warpage" because thick sections cool slower than thin ones. Draft Angles
Aris closed the notebook. He looked at his clip, then at his CAD model. He added four 0.02mm vents at the last point of fill. He adjusted the wall thickness to be uniform 2.5mm, not 2-to-5. He set the draft angle. He changed the gate to a three-pin submarine gate to balance the flow.
